During World War I, it was discovered that lignite, bituminous, or anthracite coal served as an economical source of activated charcoal or carbon, if carefully carbonized and subjected to steam activation.
Activated carbon is a microcrystalline form of carbon with a large internal surface area. This large surface area allows the physical adsorption of large quantities of impurities from gases and liquids. Activated carbons are used extensively in water and food purification, metals recovery, production of high purity gases, and flue gas cleanup.